One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult using known technology to quickly and accurately position the read/write head over the desired information tracks on the storage media. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a secondary actuator, known as a micro-actuator, that works in conjunction with a primary actuator to enable quick and accurate positional control for the read/write head. Disk drives that incorporate a micro-actuator are known as dual-stage actuator systems.
Various dual-stage actuator systems have been developed in the past for the purpose of increasing the speed and fine tuning the position of the read/write head over the desired tracks on high density storage media. Such dual-stage actuator systems typically include a primary voice-coil motor (VCM) actuator and a secondary micro-actuator, such as a PZT micro-actuator. The VCM actuator is controlled by a servo control system that rotates the actuator arm that supports the read/write head to position the read/write head over the desired information track on the storage media. The PZT micro-actuator is used in conjunction with the VCM actuator for the purpose of increasing the positioning speed and fine tuning the exact position of the read/write head over the desired track. Thus, the VCM actuator makes larger adjustments to the position of the read/write head, while the PZT micro-actuator makes smaller adjustments that fine tune the position of the read/write head relative to the storage media. In conjunction, the VCM actuator and the PZT micro-actuator enable information to be efficiently and accurately written to and read from high density storage media.
One known type of micro-actuator incorporates PZT elements for causing fine positional adjustments of the read/write head. Such PZT micro-actuators include associated electronics that are operable to excite the PZT elements on the micro-actuator to selectively cause expansion or contraction thereof. The PZT micro-actuator is configured such that expansion or contraction of the PZT elements causes movement of the micro-actuator which, in turn, causes movement of the read/write head. This movement is used to make faster and finer adjustments to the position of the read/write head, as compared to a disk drive unit that uses only a VCM actuator. Exemplary PZT micro-actuators are disclosed in, for example, JP 2002-133803, entitled “Micro-actuator and HGA” and JP 2002-074871, entitled “Head Gimbal Assembly Equipped with Actuator for Fine Position, Disk Drive Equipped with Head Gimbals Assembly, and Manufacture Method for Head Gimbal Assembly.”
FIG. 1a illustrates a portion of a conventional disk drive unit and shows a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly 100 that includes a micro-actuator 105 and a read/write head 103. A voice-coil motor (VCM) is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 103 to move from track to track across the surface of the disk, thereby enabling the read/write head to read data from or write data to the disk. In operation, a lift force is generated by the aerodynamic interaction between the slider, incorporating the read/write head, and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by a suspension of the HGA such that a predetermined flying height above the surface of the spinning disk is maintained over a full radial stroke of the motor arm 104.
FIG. 1b illustrates the head gimbal assembly 100 (HGA) of the conventional disk drive device of FIG. 1a incorporating a dual-stage actuator. However, because of the inherent tolerances of the VCM and the head suspension assembly, the slider 103 cannot achieve quick and fine position control which adversely impacts the ability of the read/write head to accurately read data from and write data to the disk. As a result, a PZT micro-actuator 105, as described above, is provided in order to improve the positional control of the slider and the read/write head. More particularly, the PZT micro-actuator 105 corrects the displacement of the slider 103 on a much smaller scale, as compared to the VCM, in order to compensate for the resonance tolerance of the VCM and head suspension assembly. The micro-actuator 105 enables, for example, the use of a smaller recording track pitch, and can increase the “tracks-per-inch” (TPI) value by 50% for the disk drive unit, as well as provide an advantageous reduction in the head seeking and settling time. Thus, the PZT micro-actuator 105 enables the disk drive device to have a significant increase in the surface recording density of the information storage disks used therein.
As shown in FIGS. 1a and 1b, one known type of micro-actuator is a U-shaped micro-actuator 105. This U-shaped micro-actuator 105 has two side arms 107 that hold the slider 103 therebetween and displace the slider by movement of the side arms. However, movement of the side arms generates a reaction force in the mounting area that will be propagated to a suspension tongue and, in turn, to the suspension itself. The reaction force causes a suspension resonance, or vibration, that will negatively impact the dynamic performance of the HGA. The suspension resonance resulting from operation of the micro-actuator is one factor that limits the bandwidth of the disk drive device.
Referring more particularly to FIG. 1c, a conventional PZT micro-actuator 105 includes a ceramic U-shaped frame which has two ceramic beams or side arms 107 each having a PZT element thereon. With reference to FIGS. 1b and 1c, the PZT micro-actuator 105 is physically coupled to a flexure 114. Three electrical connection balls 109 (gold ball bonding or solder ball bonding, GBB or SBB) are provided to couple the micro-actuator 105 to the suspension traces 110 located at the side of each of the ceramic beams 107. In addition, there are four metal balls 108 (GBB or SBB) for coupling the slider 103 to the traces 110.
FIG. 1d generally shows an exemplary process for assembling the slider 103 with the micro-actuator 105. As shown in FIG. 1d, the slider 103 is partially bonded with the two ceramic beams 107 at two predetermined positions 106 by epoxy 112. This bonding makes the movement of the slider 103 dependent on the movement of the ceramic beams 107 of the micro-actuator 105. A PZT element 116 is attached on each of the ceramic beams 107 of the micro-actuator to enable controlled movement of the slider 103 through excitation of the PZT elements. More particularly, when power is supplied through the suspension traces 110, the PZT elements expand or contract to cause the two ceramic beams 107 of the U-shape micro-actuator frame to deform, thereby making the slider 103 move on the track of the disk in order to fine tune the position of the read/write head. In this manner, controlled displacement of slider 103 can be achieved for fine positional tuning. FIG. 1e illustrates the micro-actuator and slider after being assembled as shown in FIG. 1d. FIG. 1e also shows the two possible translational movements, illustrated by arrows 117a and 117b, that the micro-actuator can produce upon excitation, as well as the resulting reaction forces (118a and 118b, respectively) generated in the base-part plate of the micro-actuator as a result of the translational movement.
While the PZT micro-actuator described above provides an effective and reliable solution for fine tuning the position of the slider, it also results in certain disadvantages. More particularly, because the PZT micro-actuator 105 and the slider 103 are mounted on the suspension tongue, a suspension resonance is generated, as a result of, for example, the reaction forces 118a and 118b, when the PZT micro-actuator 105 is excited. In other words, the translational motion of the micro-actuator used to displace the slider 103, combined with the weight of the slider and micro-actuator, causes a vibration in the suspension due to the structure and constraint of the U-shaped frame of the micro-actuator. This suspension vibration resonance resulting from operation of the micro-actuator has the same effect as the resonance of the shaking suspension base plate which will cause the slider to be off-track when the head reads data from or writes data to the magnetic disk, thereby limiting the servo bandwidth and the capacity improvement of the disk drive device.
FIG. 1f shows a graph of the resonance gain verses frequency for both the excited base plate and excited PZT element on the micro-actuator. As shown in FIG. 1f, the numeral 201 represents a resonance curve when the suspension base plate is excited and numeral 202 represents a resonance curve when the micro-actuator 105 is excited. The graph of FIG. 1f shows that under a frequency of 20 kHz, there are several large peaks and valleys in the suspension frequency response which demonstrate an adverse resonance characteristic for the device. In addition to the vibration problems, the ceramic U shaped micro-actuator of the prior art is subject to damage or malfunction when exposed to mechanical shock. In addition, the alignment and mounting procedures for the two PZT elements on the prior art micro-actuators are very complex.
Thus, there is a need for an improved micro-actuator for use in head gimbal assemblies and disk drive units that does not suffer from the above-mentioned vibration problems, yet still enables fine tuning of the read/write head.